It is known in the art that fruit juices such as citrus juices can by means of an ion exchange treatment be made to undergo a change in the perceptive acidity of such juices. Taste tests have established that the natural acidity of such juices is objectionably strong to a significant number of prospective purchasers who would prefer a less tart or sharp flavor. A process to achieve this result was first disclosed by Kilburn et al. in U.S. Pat. No. 3,165,415, filed Oct. 4, 1960 and issued Jan. 12, 1965, wherein the juice to be treated was passed through a multi-compartment electrodialysis system in alteration compartmentwise with a liquid electrolyte, the compartments being separated by an anion selective membrane permeable to passage therethrough of ions extracted from the juice and the electrolyte to thereby substitute one for the other and consequently alter the pH of the juice being treated. The process was described as equally useful for inducing an increase in the pH of a pH deficient juice, such as tomato juice, as to decrease the pH of an excessively acidic juice, such as orange or grapefruit juice, the ion permeable membrane being in the one case a film of a cation exchange resin and in the other case a film of an anionic exchange resin. The basis of this discovery was that, although the pH of natural fruit juices changes during their natural production season, the concentration of salts of weak acids which such juices contain remains substantially constant throughout such season. Hence, although the theoretical pH of any buffered solution, i.e., containing a free acid and its salts, depends upon the relative concentrations of both of the free acid and the salt, if the salt concentration remains constant, it follows that overall pH variation must in the case of citric acids be due to the free acid content of such juices. This creates the possibility for extracting proportions of the free acid content of citric and like juices by means of anion exchange or alternatively to convert citric salts to free acid by a cation exchange resin to increase the acidity for other low acid juices.
Kilburn et al. acknowledge the presence of bitterness in grapefruit juices and to some extent in some other fruit juices but give no indication of any effect on bitterness of their ion exchange treatment. Their theoretical discussion is focused on the adjustment of the levels of citric acid and citrate salts in the treated juice and the vitamin and mineral content and flavor generally are said to be unimpaired. The dialyzing membrane is designed to be selectively permeable only to either anions or cations dependent upon whether the pH of the juice was to be lowered or raised and would be impermeable to other molecules, particularly of organic flavor components.
About a decade later, research on the production of a reduced acid orange juice was spearheaded by the Coca Cola Company, Foods Division, and in the Fall of 1979, a paper was presented on behalf of that group by Dr. K. Assar, entitled "Reduced Acid FCOJ" to the Florida citrus industry, which paper was subsequently published in the "Proceedings of the 19th Annual Short Course for the Food Industry at the Institute of Food and Agricultural Sciences of the University of Florida, Gainesville, Fla." during 1980. This paper describes the efforts of this group to produce and market a reduced acid frozen concentrated orange juice obtained by an ion exchange treatment and having the approval of both Florida and federal authorities which efforts were eventually successful and led to the promulgation by both the Florida state authorities and the FDA of an approved definition for such a juice, the federal regulation appearing in CFR, Title 21--Food and Drugs--.sctn..sctn.146.150 and 173.25. The research summarized here focused on the acceptability of the reduced acid product from various health aspects, confirming the initial conclusion of Kilburn et al. that the ion exchange treatment had no significant consequences on the vitamin content of the treated juice and extending that conclusion to other nutrient components, such as ascorbic and folic acids, minerals and amino acids. The treatment in general involved passing the juice downwardly through a bed of a weak base anion exchange resin not otherwise identified.
The Assar paper refers to the practice of the Florida citrus industry of packing grapefruit juice with added sugar to render the juice more palatable but contains no mention of the bitterness of grapefruit juice as such. The concern of the program it summarizes was to develop a marketable reduced acid orange juice, and grapefruit juice apparently was never studied. Orange juice does not contain either of the principal bitter flavor components of grapefruit juice, naringin and limonin in any significant amount, if at all.
According to U.S. Pat. No. 3,801,717 to Huffman, issued Apr. 2, 1974, the development of off-flavors in citrus juices or other liquid foods during pasteurization by heating can be substantially diminished by treating the liquid in question before heating to contact with an ion exchange material, either anionic or cationic and preferably strongly cationic.